The purpose of this study are to: 1) describe the safety and tolerance of palivizumab, compared with placebo, in children with congenital heart disease and; 2) to determine palivizumab serum concentrations for all children at baseline ant at the trough after the fourth injection. Patients who are placed on cardiopulmonary bypass for surgery will have pre- and post-bypass concentrations determined to study the effect of bypass on palivizumab concentrations.